Plato's theory of Forms or theory of Ideas argues that non-physical (but substantial) forms (or ideas) represent the most accurate reality. When used in this sense, the word form or idea is often capitalized. Plato speaks of these entities only through the characters (primarily Socrates) of his dialogues who sometimes suggest that these Forms are the only objects of study that can provide knowledge; thus even apart from the very controversial status of the theory, Plato's own views are much in doubt. However, the theory is considered a classical solution to the problem of universals.